In order to obtain measurements and information from the downhole environment while drilling, the tool includes electronic devices. Downhole tools must be able to operate near the surface of the earth as well as many thousands of feet below the surface. Environmental temperatures tend to increase with depth during the drilling of the well. As the depth increases, the tools are subjected to a severe operating environment. For instance, downhole temperatures are generally high and may even exceed 200 degrees C. In addition, pressures may exceed 20,000 psi. In addition to the high temperature and pressure, there is also vibration and shock stress associated with operating in the downhole environment, particularly during drilling operations.
The electronic components in the downhole tools also internally generate heat. For example, a typical wireline tool may dissipate over 100 watts of power, and a typical downhole tool on a drill string may dissipate over 10 watts of power. Although there is electrical power dissipated by a drill string tool, the heat from the drilling environment itself still makes internal heat dissipation a problem. The internally dissipated heat must be removed from the electronic components or thermal failure will occur.